The present invention relates to a magnetic disk drive. In particular, the invention relates to an improvement in reliability of a magnetic disk drive, used in hostile environments such as for automotive use.
A magnetic disk drive has in the inside of the enclosure high precision parts such as a magnetic disk and a head for magnetic read/write as well as a spindle motor and voice coil motor that drive the magnetic disk and the head for magnetic read/write. A magnetic head flies over the high-speed rotating magnetic disk at a height of the order of nanometers and reads and writes data. A magnetic disk drive enclosure is designed so as to hinder an inflow of the external air into the enclosure to some extent because microfine dust or a trace amount of chemical substances adversely affects data read/write of the magnetic head.
On the other hand, shielding the enclosure from the external air completely changes the temperature within the magnetic disk drive, or produces pressure difference between the inside and outside of the enclosure due to changes in atmospheric pressure, which causes malfunctions such as distortion of the enclosure. As such, the magnetic disk drive is typically formed with tiny breathing holes to prevent the production of pressure difference by ensuring ventilation between the inside and outside. Providing such holes, however, readily causes the inside of the drive to be affected by the external air.
In this case, the main problem is the variation of humidity. An increase in humidity easily generates moisture condensation or the like inside, which increases possible corrosion of magnetic material of the magnetic head and magnetic disk, resulting in a decrease in product reliability. On the other hand, if the humidity within the drive is too low, static electrical charge is readily built up; as a result, the possibility of electrostatic discharge of GMR devices and the like used as the magnetic head is raised, which may result in damage.
In particular, magnetic disk drives are expected to be used in diverse environments such as for automotive use in the future, and thus the matter noted above is increasingly a serious problem. Because of this, magnetic disk drives are made to be hardly affected by external environments in many cases by placing activated carbon, silica gel or the like in the enclosure. For instance, Japanese Patent Laid-Open No. 2003-263882 (Patent Document 1) describes that a moisture absorbent placed within a magnetic disk drive effectively inhibits the moisture change and prevents malfunction due to moisture condensation, wherein the difference of the moisture absorptions in humidity values of 80% and 95% on a moisture absorption isothermal line of the moisture absorbent is 30% or more during moisture absorbing and is 20% or more during moisture discharging based on the weight of the dried moisture absorbent.
Humidity control methods with a moisture absorbent or the like, however, does not have a mechanism of discharging moisture outside, so the absorbent is saturated with water when exposed to a high humidity environment for a long period of time and loses its moisture absorbing capability, creating the problem of the inside humidity becoming finally equal to the outside humidity.
On the other hand, Japanese Patent Laid-Open No. 2-1004 (Patent Document 2) proposes a method that involves removing moisture by water electrolysis using a membrane electrode assembly. The proposed method can discharge moisture outside and has the possibility of basically solving the above problem. However, it has the problems below and is not commercialized.
(1) When the circuit is not conducted, external moisture is dispersed inside through the membrane electrode assembly, leading to a rapid increase in humidity.
(2) The inside of the magnetic disk drive is polluted by contaminants due to carbon paste used for the membrane electrode assembly.
(3) The oxygen generated during electrolysis increases the oxygen concentration inside the magnetic disk drive.
For the prevention of (1) above, it is proposed that, in FIG. 4 of Patent Document 2 mentioned above, the membrane electrode assembly be placed in the concave portion of a top and bottom two-tier structure formed substantially in the center of the base, that a first electrode of the membrane electrode assembly be disposed so as to directly come into contact with the inside of the container, and that a second electrode of the membrane electrode assembly be communicated with the outside of the container through buffer space and further via a dehumidifying port provided in the base.